The improved bid reduces the amount of debt that the merged company would hold and the interest rate on that debt, according to a report in The Wall Street Journal. Deutsche Telekom called this its "best and final offer," according to the report.

MetroPCS agreed to merge with T-Mobile USA last October in a deal that would give MetroPCS shareholders US$1.5 billion and 26 percent of the merged company. Deutsche Telekom would own 74 percent of the carrier. The new offer cuts the amount of debt that the new company will hold by $3.8 billion, to $11.2 billion, the Journal reported.

The sweetened deal comes in time for a MetroPCS shareholder vote scheduled for Friday. Some investment advisory services had recommended that MetroPCS shareholders reject the deal.

With the addition of MetroPCS, a regional carrier with about 9 million customers, T-Mobile will have approximately 42 million subscribers and a stronger portfolio of spectrum licenses for building out its national LTE network. It would remain the fourth-largest mobile operator in the U.S. behind AT&T, Verizon Wireless and Sprint Nextel.

Deutsche Telekom and T-Mobile USA were not immediately available for comment.